Heretofore, numerous test methods and apparatus have been known in the art for determining the acceptability of a tire. Force variation machines have been used to determine both lateral and radial run-out as well as tire concentricity and conicity. All of these tests have proved effective for achieving tires of improved quality for the marketplace.
It is well known that the automotive industry is presently directing its efforts to the manufacture and sale of economy cars. Such cars are substantially smaller in both size and weight than the automobiles previously supplied by the industry. These smaller vehicles are attractive due to their lesser initial cost, lighter weight, and reduced fuel consumption. This attraction has been enhanced by the usage of single-ply tires on such automobiles, such tires being of lesser cost and weight than the multiple-ply tires previously used.
While single-ply tires have become attractive for use on economy cars, certain problems inherent with those tires have become apparent. A particular problem evolves from irregularities in the ply splice at the sidewall of the tire. If this splice is other than a flush butt fit, the sidewall at the splice may exhibit undesired characteristics. For example, if the splice is lapped, the sidewall becomes exceptionally strong at that point, being effectively a double-ply at the splice. When inflated, the sidewall at the splice may not expand to the same degree as the sidewall as a whole, thus generating what is termed a "valley" in the sidewall. While this valley is an indication of exceptional strength at that point of the sidewall, if the valley is excessive it becomes unsightly and therefore unmarketable. In the case of an open splice, the sidewall is weakened such that, when inflated, the weakened area at the splice will excessively expand to define a bulge. Such a bulge is not only an indication of a weakened area in the sidewall, but becomes unsightly if excessive.
It will be appreciated that bulges and valleys are peculiar to single or mono-ply tires, since tires of multiple plies are typically of sufficient strength to be uneffected by an open or lapped splice in any of the plies. In a single ply tire an open splice results in zero ply strength at the effected area of the sidewall, while a lapped splice results in an effective doubling of the strength at that area.
While there have been several teachings in the art of apparatus for sensing and testing the dimensional characteristics of a tire, none teach the sensing and testing of bulges and valleys. Applicant is aware of U.S. Pat. Nos. 3,895,518; 3,303,571; and 2,251,803, all of which teach a technique for monitoring the sidewall of a tire. However, each of these patents is of a rudimentary mechanical nature, capable of sensing only that the sidewall of a mounted tire has exceeded the limit unassociated with the tire itself. In one such patent, a plurality of probes are positioned in a circular fashion, and a tire is placed in proximity thereto. The tire is caused to rotate and, if any of the probes are contacted, a limit switch of sorts is closed to indicate this maximum sidewall deflection. In another of the prior art teachings, an apparatus consisting of a piston and bellows is interconnected with a meter. A plurality of such devices are again spaced about the sidewall of the tire and the tire is caused to rotate. If any of the pistons are contacted by a deflection in the sidewall, the piston actuates the bellows and the amount of deflection is accordingly registered on the accompanying meter. The operator may then determine whether the deflection exceeded an allowed level.
None of the prior art teachings actually sense a deflection in the sidewall itself with respect to the sidewall as a whole. None of these prior art teachings actually sense the rate of change or the slope of the sidewall deflection. Accordingly, none of the prior art systems can truly sense the presence or absence of bulges or valleys in sidewalls, but can only sense whether or not a portion of the sidewall has exceeded some preset lateral limit.